Until two weeks ago, biology teacher Gill Arbuthnott led a secret life. By day she stood at the front of her class at Edinburgh Academy talking about the process of photosynthesis, the shape and structure of bones and so on, and by night she was creating magical tales for children.

After the 9pm marking and bedtime watershed - Gill is also a mother of two - she was, as she puts it, secretly “scribbling away”. She even admits to keeping a piece of school work beside her to hastily pull over her writing in case of interruptions.

Now this closely guarded secret has been rumbled. At the end of October Floris Books, the Edinburgh-based publishers who own the much loved Kelpie range, launched her first children’s novel, The Chaos Clock, and her success has come as a complete surprise for her family, friends and school colleagues.

This was the first new Kelpie book for eight years. “I sent it to Kelpie because I had always been impressed by the quality of their books,” says Gill, “and after that things happened very fast.”

Too modest to admit to anyone that her book had been snapped up, Gill has had to adjust not only to her long-held secret being out, but also to coping with interviews, readings and questions.

The contrast between the solitary activity of writing and the sense of public ownership after publication is well known to writers and the adjustment can be difficult. In Gill’s case, the fact that she had been a secret writer since her student days in St Andrews has made her turn in the spotlight even harder.

“As a pupil at school I was not such a closet writer,” she explains.

“English was as important for me as biology, but as soon as I became a scientist it was a secret from parents, friends and later from my husband, Tom.

“As writing was an untutored, private activity for me, I was able to develop my own ways of working, which I think has been an advantage. I have always felt that I was writing for myself and I have tried to curb my melodramatic tendencies.”

The Chaos Clock is certainly a dramatic read, well crafted, well sustained and imaginative. Aimed at eight- to 13-year-olds, it tells the story of two 11-year-old Edinburgh school friends, Kate and David, who, while doing a museum project together, become embroiled in a dark struggle between the Lords of Chaos and the Guardians of Time. The Millennium Clock in the Royal Museum is central to the plot.

“I have always loved the museum, ever since childhood,” says Gill. “After one of my visits, I began to explore in my writing the idea of the power of objects from the past, how little we really know, how little we probably understand of this power. This idea of power and time stayed with me, fermenting away, until I thought of using the Millennium Clock, which really pulled everything together. Visually, it is so strong, dark and other-worldly, and you can see how it fascinates all ages when it strikes.

It became the focal point for the book.”

It was at this point that she realised it was going to be a book for older children rather than adult fiction.

Ideas, incidents, phrases, names and places all came first before Kate and David presented themselves to her as the central characters. They are wholly imagined, but their friendship is based on that between her daughter, Ellen, and her friend, Michael, and its feeling of unforced authenticity is one of the strengths of the story. The relationships within the two families are also utterly convincing, written without affectation or self-consciousness.

Teaching has not affected or unduly influenced her writing, Gill believes, although she concedes she has paid particular attention to how her pupils speak, the rhythms and words that they use.

“The classroom is a brilliant hothouse in which to study the authenticity of relationships, how they change with age, how friends speak to each other,” she says.

“It is also an endless repository of names; like Flowerdew, taken from an ex-pupil and put to good use in the book.”

Literary agent and children’s books expert Lindsey Fraser says: “A lot of teachers try to write but there is a very, very, very long journey between trying to write and getting to where Gill is. Most seem to write as a way to escape from teaching, whereas Gill wants to continue both.”

She praises The Chaos Clock, especially the vivid descriptions of the other worlds that haunt the story.

“Children’s publishing went down the gritty realism route for a time and now we have learned that fantasy is the way to their hearts.”

The Chaos Clock, a contemporary Kelpie novel by Gill Arbuthnott (Floris Books, pound;4.99). A teacher’s guide to accompany the book, with suggestions for group activities, individual work and class visits is available onlinewww.florisbooks.co.ukteachers.html